Literature Review of Abalone Ageing Techniques. New Zealand Fisheries Assessment Report 2015/77
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Literature review of abalone ageing techniques New Zealand Fisheries Assessment Report 2015/77 R. Naylor ISSN 1179-5352 (online) ISBN 978-1-77665-125-2 (online) December 2015 Requests for further copies should be directed to: Publications Logistics Officer Ministry for Primary Industries PO Box 2526 WELLINGTON 6140 Email: [email protected] Telephone: 0800 00 83 33 Facsimile: 04-894 0300 This publication is also available on the Ministry for Primary Industries websites at: http://www.mpi.govt.nz/news-resources/publications.aspx http://fs.fish.govt.nz go to Document library/Research reports © Crown Copyright - Ministry for Primary Industries Contents Executive Summary ....................................................................................................... 1 1 Objectives ............................................................................................................... 1 2 Methods .................................................................................................................. 1 3 Shell structure and growth...................................................................................... 1 4 Ageing techniques .................................................................................................. 4 5 Validation methods ................................................................................................. 9 6 Acknowledgements .............................................................................................. 12 7 References ............................................................................................................ 13 EXECUTIVE SUMMARY Naylor, R. (2015). Literature review of abalone ageing techniques. New Zealand Fisheries Assessment Report 2015/77. 17 p. The estimation of age in abalone using shell growth rings has been achieved using two main techniques. These are the counting of external growth checks on the shell and the counting of internal growth checks within sections of the shell. The internal growth checks may also be viewed by grinding the spire and viewing the checks as a series of concentric rings. External daily growth increments have been validated in H. madaka. Age in abalone has also been estimated by a few authors using stable oxygen isotopes. Stable oxygen isotope analyses appear to be the most reliable method of validating the timing of growth check deposition. Commonly used methods of validation such as age estimation from tag-recapture data or the use of length frequency data to determine age are flawed because of the inherent variability of the data. 1 OBJECTIVES OVERALL OBJECTIVE: 1. To conduct a literature review on abalone ageing techniques using growth rings. SPECIFIC OBJECTIVES 1. To provide a conceptual description of abalone shell structure and growth. 2. To describe different techniques which have been used to age abalone using shell growth rings or any other morphological characteristics of the shell. 3. To describe the different methods which have been used to validate ageing of abalone using shell growth rings or any other morphological characteristics of the shell. 2 METHODS The primary sources of information for this review were web-based search engines such as Google Scholar, Scopus, and the ISI Web of Knowledge. Literature that the author was aware of was also consulted. Once relevant articles were found, their bibliographies were examined to identify older articles on the subject, and more recent articles were found by examining papers which had cited that article. The information was then summarised and discussed. The utility of various methods is also discussed. Where appropriate, the theoretical basis for particular methodologies is also presented. 3 SHELL STRUCTURE AND GROWTH Mollusc shells are constructed primarily from carbonate in the form of calcite, aragonite, or both (Jones et al. 1983). Calcite and aragonite both have the same chemical formula (CaCo3) but the two polymorphs have a different crystal structure (Heinemann et al. 2011). The shell of paua (Haliotis iris) is composed of a very fine outer layer of protein (the periostracum) which is about 100–200 nm thick, an outer layer of prismatic calcite and inner layers of nacreous aragonite separated by thin layers of protein (Gray & Smith 2004, Figure 1). In older shells the periostracum is frequently eroded. Ministry for Primary Industries Literature review of abalone ageing techniques 1 The prismatic calcite layer contains rhomboidal calcite crystals (up to 100 nm in diameter) surrounded by a very thin (0.5–3 nm) glycoprotein matrix (Gray & Smith 2004). The inner aragonite layers, usually referred to as nacre, comprise stacks of flat shingle-like crystals or tiles, layered on top of one another, and surrounded by an organic matrix (Gray & Smith 2004, Figure 2). The tiles initially stack up as pyramids, and lateral growth of the tiles continues until the tile layer is continuous (Heinemann et al. 2011, Figure 3). The aragonite layers are periodically separated by a protein layer laid down along the length of the shell. These layers mark interruptions in the deposition of aragonite (Meyers et al. 2008). Sumitomo et al. (2011) examined these layers in H. gigantea, and found that they acted mechanically like aragonite, but were much stronger. The abrupt transition between aragonite and this layer also suggests that abalone are able to rapidly alter the biomineralisation process (Sumitomo et al. (2011). Epiphytic cora lline a lga e Prismatic calcite layer Ara gonite la yers Pro te in la ye rs Figure 1: A magnified (about 12 ×) longitudinal cross section of a paua shell. The outer periostracum is not evident and the top of the shell has been colonised by coralline algae. Figure 2: Scanning electron microscope image (magnified about 1000 ×) of a cross section of paua shell showing a protein layer (centre) surrounded by layers of aragonite tiles. Reprinted from Catch, with permission from the Ministry of Fisheries. They suggested that this layer serves a protective role during periods of unfavourable conditions or during conditions of lifecycle transition (Sumitomo et al. (2011). In paua, the thickness of the aragonite tiles is locally very regular over hundreds of tiles, but between the protein layers there 2 Literature review of abalone ageing techniques Ministry for Primary Industries appears to be a cyclical variation in tile thickness between about 0.25 and almost 0.5 µm., where just before, and just after the protein layers, the tile thickness is the lowest (Snow & Pring 2005). The structure of the calcite and aragonite layers is essentially similar to that in brick and mortar construction where the protein is the mortar. Calcium carbonate alone is not suitable as a structural material because it is inherently brittle (Meyers et al. 2008). The laminated composite form is a highly ordered hierarchical structure, which affords the shell fracture toughness eight times that of monolithic calcium carbonate (Sarikaya et al. 1990). Pe ri o st ra c u m Prismatic calcite Na c re (tile s) Extrapallial space Mantle epithelium Figure 3: Schematic representation (not to scale) of a vertical cross section of abalone shell. After Heinemann et al. (2011). New material is added to the outer edges of the shell and to the inside of the shell so that the shell becomes thicker as it becomes larger, and the direction of growth is in the form of a logarithmic spire (Sinclair 1963, i.e. the whorls continually increase in breadth in an unchanging ratio, see Figure 5). The iridescence (i.e. the way the way the shell changes colour when you look at it from different angles) is caused by the diffraction of light and interference to it, when it passes through the aragonite tiles that comprise the nacre. The thickness of the tiles apparently influences the colour appearance of nacre, eg. thin tiles give the shell a mainly blue appearance and with thicker tiles, only green and red colours are seen (Snow & Pring 2005). The precipitation of shell material occurs within the extrapallial space between the shell (or periostracum) and the mantle (Lin & Meyers 2005, Figure 3). The mantle is a soft, thin sheet of tissue next to the shell that surrounds the adductor muscle at its attachment point and covers the body organs. The periostracum seals the extrapallial space and also provides support for the first layers of calcite deposited (Marin & Luquet 2004). Region of new nacre growth Pro t e in la ye r Figure 4: Photograph of the inside of a paua shell (135 mm in length) showing the area of nacre deposition and the protein layer. The region of nacre deposition is characterised as being dull. Ministry for Primary Industries Literature review of abalone ageing techniques 3 Calcium and bicarbonate ions are taken up by the gills, gut, mantle epithelium, or body surface, from the surrounding water and transported to the epithelial cells where they are stored until required (Marin & Luquet 2004). They are then actively pumped from the mantle epithelium into the sealed extrapallial space to form a supersaturated solution which allows the crystallisation of calcium carbonate (Marin & Luquet 2004). A calcifying matrix is also secreted into the extrapallial space and this interacts with the mineral ions such that they self assemble in a precise manner to form crystals with well defined morphologies (Marin & Luquet 2004). The calcifying matrix is also thought to be the main nucleating agent (i.e. involved in the formation of a focal centre around which the crystal lamellae can